JP5315980B2 - Droplet ejection apparatus, droplet ejection method, and image forming apparatus - Google Patents

Description

  The present invention relates to a droplet discharge apparatus, a droplet discharge method, and an image forming apparatus. Specifically, for example, a serial type printing apparatus that mounts an inkjet head on a carriage and performs printing while reciprocating, and an inkjet head on a line. Drop-on-demand type liquid droplet ejection device for forming an image using a line head type printing device that prints in a state where it is installed in a color liquid or organic material used for manufacturing a color filter for a liquid crystal display The present invention relates to a drop-on-demand type droplet discharge device that ejects a special liquid such as an electrode material liquid used for forming an electrode film such as an EL display.

Recent printing apparatuses using drop-on-demand ink jet heads can output high-definition images comparable to photographic image quality at high speed. This is because the ink droplets ejected from the nozzle openings are becoming finer and small ink droplets are selectively ejected onto the recording medium in the range of 1 picoliter (10 ^-12 liters) to 30 picoliters to output an image. Is going.

  As described above, various techniques for changing a large droplet and an ink droplet from small droplets have been proposed. For example, it has a first drive pulse that can eject a relatively small amount of ink and a second drive pulse that can eject a larger amount of ink than the ink droplet formed by the first drive pulse. In order to obtain ink droplets, a technique has been proposed in which the first pulse and the second pulse are continuously driven to combine when the ink droplets land on the recording medium to form larger ink droplets. (See Patent Document 1; Japanese Patent Laid-Open No. 11-20165). However, the driving pulse for forming each ink droplet is very complicated, the period for ejecting the ink droplet becomes long, and the increase in printing speed becomes a problem.

  In view of such a problem, a plurality of drive pulses are continuously configured, and a plurality of drive pulse intervals are set to be close to the natural period determined by the shape of the pressure generation chamber and the ink supply path communicating with the nozzle opening. There has been proposed a technique for forming droplets to increase the speed and improve the image quality (see Patent Document 2; Japanese Patent Application Laid-Open No. 2007-62326). However, even if this method is used, if the number of continuous drive pulses increases, the flight distance of the ink droplets until the ink droplets merge is increased.

In order to further increase the speed, a resonance drive pulse using the resonance of the natural period and a non-resonance drive pulse not using the resonance of the natural period are used as a plurality of continuous drive pulses. Ink ejected by a plurality of drive pulses by taking an interval of m × Tc (m ≦ 2) and non-resonant pulses by taking a pulse interval of (m + 1/4) × Tc to (m + 3/4) × Tc. There has been proposed a technique for changing the amount of ink droplets by combining the droplets during flight (see Patent Document 3; Japanese Patent Application Laid-Open No. 2007-182061).
Japanese Patent Laid-Open No. 11-20165 JP 2007-62326 A JP 2007-182061 A

  In the case of Patent Document 2, as the number of continuous driving pulses increases as described above, the flying distance of the ink droplets until the ink droplets merge is increased. When the flying distance of the ink droplets becomes long, the flying speed of the ink droplets decreases due to air resistance and disturbance, and there is a problem that the straightness is impaired and the printing quality is deteriorated.

  In the case of Patent Document 3, the use of a resonance drive pulse and a non-resonance drive pulse needs to be optimized more for the operation of generating a drive pulse and for stable ejection. Further, the movement of the meniscus varies greatly depending on the viscosity of the ink, which causes a problem that print quality is deteriorated.

  The present invention has been made in view of these problems, and a first object of the present invention is to provide a droplet discharge apparatus and a droplet discharge method capable of increasing the droplet discharge speed and having high droplet landing quality. It is to provide.

  A second object is to provide an image forming apparatus capable of highly accurate dot gradation recording.

In order to achieve the first object, the first means of the present invention comprises:
A nozzle opening provided for discharging liquid, a pressure generating chamber provided in communication with the nozzle opening, pressure generating means for expanding and contracting the volume of the pressure generating chamber, and A liquid droplet ejection head having a fluid resistance portion provided in the middle of a liquid flow path for supplying liquid;
A drive control unit that applies a drive pulse for expanding and contracting the volume of the pressure generating chamber to the pressure generating unit;
Two or more drive pulses are continuously applied from the drive control unit at a predetermined interval to the pressure generating means, and the liquid droplets ejected according to the number of drive pulses substantially before reaching the adherend. The present invention is intended for a droplet discharge device that merges into one droplet and lands on the adherend medium.

The drive control unit
Output drive pulses with the same pulse shape,
When the period of the natural frequency determined by the liquid flow path from the nozzle opening to the fluid resistance part is Tc, the pulse width Tp of the drive pulse is set smaller than the period Tc (Tp <Tc),
When the pulse interval from the start of the nth pulse to the start of the (n + 1) th pulse of n consecutive (n ≧ 2) integer driving pulses is TNn, the first pulse with n = 1 and n = 2 The pulse interval TN1 with the second pulse is set in a range of 1.2 × Tc to 1.5 × Tc, and the pulse interval TN2 after the pulse interval TN2 between the second pulse and the next third pulse is set. , TN3,... TNn is smaller than TN1 and set to a period Tc or more of the natural frequency of the liquid flow path (TN1 = 1.2 × Tc to 1.5 × Tc> (TN2, TN3,..., TNn ≧ Tc).

  According to a second means of the present invention, in the first means, the pulse interval after the pulse interval TN2 is sequentially reduced, and the final pulse interval TNn is greater than or equal to the period Tc of the natural frequency of the liquid channel. It is set (TN2> TN3>...> TNn ≧ Tc).

  According to a third means of the present invention, in the first or second means, the driving pulse is set so that the expansion time Tf when the voltage is raised to expand the volume of the pressure generating chamber and the raised voltage is constant. It has a trapezoidal waveform having a holding time Th for holding and a contraction time Tr for decreasing the voltage in order to contract the volume of the pressure generating chamber.

  According to a fourth means of the present invention, in the third means, the total time Tw of the expansion time Tf and the holding time Th is drawn by the expansion of the pressure generation chamber, and the drawing position of the meniscus is approximately 1 / It is characterized in that it is within the time range from the point of 2 until the meniscus position first becomes the lowest point.

  According to a fifth means of the present invention, in the first to fourth means, a contact angle of the surface of the nozzle opening with respect to the liquid is 65 ° or more.

  According to a sixth means of the present invention, in the first to fifth means, the plurality of droplets ejected in accordance with the number of drive pulses is not less than ½ of the distance from the nozzle opening to the adherend medium. One droplet is formed in a range from a position exceeding the range to the deposition medium.

  According to a seventh means of the present invention, in the first to fifth means, the plurality of droplets ejected in accordance with the number of drive pulses has a distance from the nozzle opening to the deposition medium of 0.5 mm to One droplet is formed within a range of 2 mm.

According to an eighth means of the present invention, in the first to seventh means, the last droplet of the plurality of droplets ejected according to the number of driving pulses reaches the last of the adherend medium. The time difference until the droplets land on the adherent medium is Ts, and the speed of the adherent medium of the line head type device or the serial type carriage speed is Vp. When the distance to the center of the droplet is Ln, the time difference Ts between the first droplet and the last droplet is Ts = Ln / Vp or less .

  According to a ninth means of the present invention, in the first to eighth means, a heater is installed in the droplet discharge head, and the temperature is controlled so that the viscosity of the discharged liquid becomes substantially constant. It is what.

In order to achieve the first object, the tenth means of the present invention comprises:
A nozzle opening provided for discharging liquid, a pressure generating chamber provided in communication with the nozzle opening, pressure generating means for expanding and contracting the volume of the pressure generating chamber, and A droplet discharge head having a fluid resistance portion provided in the middle of a liquid flow path for supplying a liquid;
Two or more drive pulses are continuously applied to the pressure generating means at a predetermined interval, and the liquid droplets ejected in accordance with the number of drive pulses become substantially one liquid droplet before reaching the adherend medium. The present invention is intended for a droplet discharge method that combines and land on the adherend medium.

And the continuous drive pulses have the same pulse shape,
When the period of the natural frequency determined by the liquid flow path from the nozzle opening to the fluid resistance part is Tc, the pulse width Tp of the drive pulse is set smaller than the period Tc (Tp <Tc),
When the pulse interval from the start of the nth pulse to the start of the (n + 1) th pulse of n consecutive (n ≧ 2) integer driving pulses is TNn, the first pulse with n = 1 and n = 2 The pulse interval TN1 with the second pulse is set in a range of 1.2 × Tc to 1.5 × Tc, and the pulse interval TN2 after the pulse interval TN2 between the second pulse and the next third pulse is set. , TN3,... TNn is smaller than TN1 and set to a period Tc or more of the natural frequency of the liquid flow path (TN1 = 1.2 × Tc to 1.5 × Tc> (TN2, TN3,..., TNn ≧ Tc).

  According to an eleventh means of the present invention, in the tenth means, the pulse interval after the pulse interval TN2 is sequentially reduced, and the final pulse interval TNn is greater than or equal to the period Tc of the natural frequency of the liquid channel. It is set (TN2> TN3>...> TNn ≧ Tc).

  A twelfth means of the present invention is the tenth or eleventh means according to the tenth or eleventh means, wherein the drive pulse includes a time Tf of an expansion step for raising a voltage to expand the volume of the pressure generating chamber, and a rise voltage. It has a trapezoidal waveform shape having a holding process time Th for holding constant and a contraction process time Tr for decreasing the voltage in order to contract the volume of the pressure generating chamber.

  According to a thirteenth means of the present invention, in the twelfth means, the total time Tw of the time Tf of the expansion step and the time Th of the holding step is drawn by the expansion of the pressure generating chamber, and the meniscus drawing position Is within the time range from the point at which the ratio becomes approximately ½ until the meniscus position first becomes the lowest point.

  According to a fourteenth means of the present invention, in the tenth to thirteenth means, a contact angle of the surface of the nozzle opening with respect to the liquid is 65 ° or more.

  According to a fifteenth means of the present invention, in the tenth to fourteenth means, the plurality of droplets ejected in accordance with the number of drive pulses is ½ or more of the distance from the nozzle opening to the adherend medium. One droplet is formed in a range from a position exceeding the range to the deposition medium.

  According to a sixteenth means of the present invention, in the tenth to fifteenth means, the plurality of droplets ejected in accordance with the number of drive pulses has a distance from the nozzle opening to the deposition medium of 0.5 mm to One droplet is formed within a range of 2 mm.

A seventeenth means of the present invention is the tenth to fifteenth means according to the tenth to fifteenth means, wherein the first droplet of the plurality of droplets ejected according to the number of drive pulses reaches the last of the deposition medium after reaching the adherend medium. The time difference until the droplets land on the adherent medium is Ts, and the speed of the adherent medium of the line head type device or the serial type carriage speed is Vp. When the distance to the center of the droplet is Ln, the time difference Ts between the first droplet and the last droplet is Ts = Ln / Vp or less .

  According to an eighteenth means of the present invention, in the tenth to seventeenth means, a heater is installed in the droplet discharge head, and the temperature is controlled so that the viscosity of the discharged liquid becomes substantially constant. It is what.

  In order to achieve the second object, according to a nineteenth means of the present invention, in the image forming apparatus, the liquid is an ink, the landing medium is a recording medium, and the first to ninth means. A droplet discharge device is provided.

  According to a twentieth means of the present invention, in the nineteenth means, a plurality of droplet discharge heads each loaded with inks of different colors such as cyan, magenta, yellow and black are provided. Is.

The present invention is configured as described above, and can provide a droplet discharge apparatus and a droplet discharge method that can increase the droplet discharge speed and that have high droplet landing quality.
In addition, the present invention can provide an image forming apparatus capable of highly accurate dot gradation recording.

  Hereinafter, an ink jet recording apparatus will be described as a representative example of the present invention. In the present invention, in an ink jet recording apparatus that controls the amount of ink droplets by multi-pulse driving, it is possible to apply substantially the same driving pulse waveform without extremely increasing the entire width of the driving pulse applied to the pressure generating means. The relationship between the movement of the meniscus of the nozzle opening and the natural period of the recording head is intended to land the ink droplets that are continuously ejected as a substantially single ink droplet before reaching the recording medium. By using, dot gradation recording can be performed stably in a high drive frequency range.

  FIG. 5 is a perspective view of the ink jet recording apparatus according to the embodiment of the present invention. This embodiment is an example of a desktop type small serial scan printing method, but it may be a so-called wide format printer which is a printing apparatus for a large format recording medium such as a poster, or a line printing method in which a plurality of recording heads are fixed side by side. The present invention applies. The ink jet recording head of the present invention is also applied to a discharge head used for a dispenser, an ink jet type three-dimensional modeling machine, and the like used for industrial purposes other than a printing apparatus.

  In the figure, 1 is an ink jet recording head, 100 is a recording medium, 101 is a sub ink tank, 102 is a head maintenance unit, 103 is a main ink tank, 104 is a supply tube, 105 is a cap, and 110 and 111 are guide shafts. It is.

  The recording head 1 is connected to a timing belt (not shown) and reciprocates on guide shafts 110 and 111 extending from the frame by forward and reverse rotation of a driving motor, and ejects ink droplets onto the recording medium 100 to thereby print characters and graphics. Etc. Ink supply to the recording head 1 is sent from the main ink tank 103 to the sub ink tank 101 via the supply tube 104. Further, the ink is supplied to the recording head 1 through the supply tube 104. The head maintenance unit 102 removes the cap 105 or the ink attached to the nozzle surface (not shown) to prevent ink drying from the nozzles of the recording head 1 and adhesion of foreign matter when printing is not performed. For example, a wiper blade is provided. The cap 105 is also used as a suction cap when the ink is filled into the recording head 1 from the sub ink tank 101 or when a purging operation is performed for the purpose of removing bubbles stagnated in the recording head 1. The

  FIG. 1 is a cross-sectional view of a multilayer ink jet recording head according to Embodiment 1 of the present invention. The ink jet recording head 1 includes a nozzle plate 10 having a plurality of nozzle openings 11 in at least one row in a direction perpendicular to the paper surface, and a chamber plate 20 having a communication channel 21 communicating with the nozzle openings 10; A restrictor plate 30 having an opening hole 33 that also serves as the restrictor 32 and the pressure generating chamber 31, a thin diaphragm plate 40 that seals the pressure generating chamber 31 and the restrictor 32, and only the pressure generating chamber 31 portion. In order to greatly displace, the support plate 50 having an opening hole in the ink reservoir 52 common to the region where the diaphragm plate 40 is held as the vibration plate 41, and the entry of foreign matter into the flow path to each nozzle opening 11 are prevented. The flow path substrate 5 is composed of a filter plate 60 having a filter 61 provided for the purpose. It has been.

  Furthermore, the flow path substrate 5, a high-rigidity plate 70 having a common ink chamber 71 that holds the flow-path substrate 5 and introduces and stores ink from the outside, and an opening groove 72 opened in the high-rigidity plate 70 A piezoelectric actuator 80 having a plurality of divided piezoelectric vibrators 81 is fixed to the diaphragm 41.

  The nozzle plate 10 is drilled with high accuracy in order to obtain the straightness of flying ink droplets, and is formed by a method of drilling a nickel electroforming method or a stainless steel thin plate by a precision press method. The chamber plate 20 is formed with a communication channel 21 whose longitudinal direction is shorter than a hole formed in the restrictor plate 30. The nozzle opening hole 11 is located on the end side of the communication channel 21. The restrictor plate 30 is provided with elongated openings serving as flow paths for the pressure generating chamber 31 and the restrictor 32.

  The present embodiment is an example in which the nozzle openings 11 are arranged in one line in a direction perpendicular to the paper surface. However, even if a plurality of lines are arranged in one recording head, the nozzle openings 11 are arranged on the inner side, and the pressure is set. The flow passage holes such as the generation chamber 31 may be arranged so as to face each other. The communication flow path plate 20 and the chamber plate 30 are formed by processing a thin stainless steel plate by an etching method or a precision press method. Alternatively, a silicon wafer may be formed by an anisotropic etching method or a dry etching method.

  The diaphragm plate 40 that seals the pressure generating chamber 31 and the restrictor 32 is a thin plate made of a stainless steel plate made of a thin plate or a nickel material by an electroforming method, compared to other plates. Or after laminating | stacking a thin plastic film or this plastic film and a thin metal plate, you may etch and remove the metal plate of the area | region part used as a diaphragm. The support plate 50 can also be formed by processing a thin stainless steel plate by an etching method or a precision press method. The high-rigidity plate 70 can be easily formed by cutting a stainless bar or the like.

  The piezoelectric actuator 80 fixes a bulk state piezoelectric vibrator 81 (piezoelectric element) in which a conductive material and a piezoelectric material are alternately laminated to one end side of a support member 82, and the bulk piezoelectric vibrator 81 is attached to each of the individual members. The piezoelectric vibrator 81 is divided into a plurality of piezoelectric vibrators 81 so as to correspond to the pressure generating chambers 31, and the end faces of the piezoelectric vibrators 81 are in contact with and fixed to the diaphragm 41. The piezoelectric vibrator 81 exemplified in this example is of the d33 type that is most displaced in the stacking direction, but may be of the d31 type that is displaced in the stacked vertical direction, or a thin plate piezoelectric body is used. It may be the method. Alternatively, instead of the piezoelectric actuator 81, an electrostatic system may be used as the displacement conversion means. The piezoelectric vibrator 81 is connected to a drive control unit 83 that outputs a drive pulse as described later.

  Next, an operation process in which ink droplets are ejected from the ink jet recording head 1 will be described with reference to FIGS. FIGS. 2A to 2D are diagrams showing an example of an ink jet recording head having the simplest laminated structure, and FIG. 3 shows an example of a driving pulse used for ejecting a droplet from a nozzle opening. FIG.

  As shown in FIG. 2A, in the state where the ink flow path is filled with the ink 6, the drive pulse 7 is driven by the piezoelectric vibrator 81 with a predetermined potential difference V from the drive control unit 83 (not shown). When applied from the control unit, the piezoelectric vibrator 81 contracts and the diaphragm 41 of the diaphragm plate 40 is deformed. As a result, the volume of the pressure generation chamber 31 expands, and the ink 6 is supplied from the common ink chamber 71 to the pressure generation chamber generation chamber 31 via the restrictors 32. At the same time, the ink meniscus at the nozzle opening 11 is also pulled back to the pressure generating chamber 31 side (see FIG. 2B). Such a process is hereinafter referred to as an expansion process, and the time is Tf (see FIG. 3).

  When the voltage is held as it is, the meniscus pull-in is completed (hereinafter referred to as a holding step, and the time is referred to as Tp, see FIG. 3), and it tries to return to the outlet side of the nozzle opening 11 again. At this point, the voltage is released in a shorter time than the expansion step in the direction in which the piezoelectric vibrator 81 extends (hereinafter referred to as the contraction step, and the time is referred to as Tr, see FIG. 3). Then, the ink 6 filled in the pressure generating chamber 31 is compressed by the expansion step, and the pressure generating chamber 31 is in a high atmospheric pressure state, and the pressure of the ink 6 increases (see FIG. 2C). This pressure causes ink droplets 8 to fly from the nozzle openings 11 (see FIG. 2D).

  FIG. 4 shows the movement of the meniscus, which is the ink surface of the nozzle opening 11 when a weak driving pulse 9 that does not eject ink droplets is applied to the ink jet recording head 1, as observed by a laser Doppler device.

  The drive pulse 9 is applied with a signal 9a for expanding the pressure generating chamber 31, and keeps the state, and when the meniscus is restored to its original position, a signal for releasing the expansion is given and observed. The meniscus movement is greatly drawn by the expansion of the pressure generation chamber 31. Thereafter, if the expansion is kept, the meniscus begins to return to the nozzle opening 11 while vibrating. It is a well-known fact that the natural period Tc, which is the vibration period, is a natural frequency period Tc determined by the ink flow path from the restrictor 32 to the nozzle opening 11. Here, as a result of determining the restrictor 32 and the pressure generating chamber 31 with the opening diameter of the nozzle opening 11 being 28 μm and the pitch of the nozzle opening holes 11 being 1/150 dpi (dot per inch), approximately 140 kHz = 7.5 microseconds. The period Tc of the natural vibration was obtained.

  Next, a multi-pulse driving method for controlling the amount of ink droplets will be described in detail. FIG. 6 shows an example of a driving pulse waveform when a driving pulse is continuously applied five times to the recording head 1 in which the meniscus of FIG. 4 is observed.

  Each drive pulse 7a and 7b has an expansion process time Tf for expanding the volume of the pressure generating chamber 31 for 2 microseconds, a retention process time Th for maintaining the expanded state is 2.5 microseconds, and an ink drop. The contraction process time Tr for contracting the volume of the pressure generating chamber 31 for discharging from the nozzle opening is 2 microseconds, and the total time Tp of the expansion process, the holding process, and the contraction process (see FIG. 3) is 6 .5 microseconds. The shape of the drive pulse is trapezoidal, but it may be a triangular drive pulse without the holding step Th.

  Here, the total time Tw of the time Tf of the expansion process and the time Th of the holding process is such that the meniscus is pulled in by the expansion process, and the meniscus pulling position becomes the lowest point first from the point where the meniscus pulling position becomes almost ½. It is preferable that the time is within the range up to a certain point. This is because the discharge efficiency can be increased by using the energy when the meniscus is drawn into the pressure generating chamber 31 side.

  As shown in FIG. 6, the interval between successive drive pulses is TN1, TN2,. When the amount of ink droplets to be ejected is varied by applying drive pulses continuously and performing multi-drive in this way, the drive pulse interval is preferably short in order to increase the drive frequency. Accordingly, the total drive pulse time Tp is made smaller than the natural frequency period Tc determined by the liquid flow path from the nozzle opening 11 to the wrist reactor 32 (fluid resistance portion) (Tp <Tc).

  FIGS. 7A to 7C show driving pulses for the natural frequency period Tc (= 7.5 microseconds) determined by the liquid flow path from the nozzle opening 11 to the wrist reactor 32 (fluid resistance portion). The drive pulse interval TN when continuously driven under the condition that the total time (pulse width) Tp is slightly shortened (= 6.5 microseconds) is 7.5 microseconds (FIG. 7A), and 8. 5 microseconds [FIG. 7B], 9.0 microseconds [FIG. 7C], the number of drive pulses and the ink droplet ejection speed when five drive pulses are applied continuously at the same interval. The relationship is shown. Here, the ejection speed represents the average speed of the ink droplets from when the tip of the ink droplets to be ejected is about to jump out of the nozzle opening 11 until reaching the recording medium.

  8A to 8C show the flying state of the ink droplets corresponding to FIGS. 7A to 7C, and ¼ point in time of reaching 1 mm after the ink droplets are ejected. The state when the head of the ink droplet reaches approximately 1 mm from the nozzle opening 11 is shown.

  As shown in FIGS. 7A to 7C, the ink droplet ejection speed gradually increases as the number of continuous drive pulses increases. It can also be seen that the longer the TN, the smaller the amount of change. However, as shown in FIGS. 8A to 8C, if the TN becomes too long, the subsequent ink droplet cannot catch up with the previous ink droplet. This is because the meniscus which is the ink surface of the nozzle opening 11 is vibrated by the first ink droplet ejected by the first drive pulse. The meniscus continues to vibrate after the ink droplets are ejected. The ejection speed of the second ink droplet ejected by the next applied drive pulse is greatly affected by the position of the meniscus in the first drive pulse, that is, depending on the speed and direction of the meniscus. Because it is done.

  In the case of forming an image by selectively extracting from continuous drive pulses, it is desirable that the change in the ink droplet ejection speed is small from the viewpoint of ink droplet landing position, that is, image quality improvement. That is, when the ink droplet is landed on the recording medium, it is preferable to fly at least to the extent that the dots are not separated. More preferably, it is desirable that the ejection speed of the ink droplet does not change regardless of which drive pulse number is selected.

  In FIG. 9A, two continuous drive pulses are applied, and the drive pulse interval (pulse pitch) is 7.8 microseconds, 8.2 microseconds, 8.5 microseconds, 9 microseconds, 9.5 microseconds. FIG. 9 (a1) shows the relationship with the speed when the ink droplet ejected at that time flies over a distance of 1 mm. Show.

  When the pulse interval is short, the ink droplets ejected continuously fly as one droplet almost simultaneously when ejected from the nozzle opening 11. As the drive pulse interval is increased, the distance until two drops collide increases. When the ink droplet collision approaches 1 mm, the speed becomes almost constant. From this result, when the printing gap (interval from the surface of the nozzle plate 10 to the recording medium) is about 1 mm, the ink droplets are only one, and the ink droplet speed is about 8 m / s, and the drive pulse interval Those having a TN1 condition of 9 microseconds were selected. This is 1.2 times the natural period Tc = 7.5 microseconds (1.2 × Tc).

  Next, in FIG. 9B, three continuous drive pulses are applied, and the drive pulse interval (pulse pitch) is 8 microseconds, 8.5 microseconds, 8.7 microseconds, 8.9 microseconds, 9 microseconds. FIG. 9B1 shows the relationship between the interval between the second drive pulse and the third drive pulse and the speed of the ink droplet. Here, the interval TN1 between the first drive pulse and the second drive pulse is selected to be 9 microseconds. Similarly, the driving pulse interval TN2 in the vicinity where the ink droplet velocity is 8 m / s is selected to be 8.7 microseconds. Although not shown in the figure, the interval between drive pulses in the case of four consecutive drive pulses and five consecutive pulses is determined based on the same concept.

  FIG. 10A shows the flying state of ink droplets when five driving pulses are applied continuously, FIG. 10B shows the relationship between the number of driving pulses and the speed of ink droplets, and FIG. The relationship between the number of pulses and the ink droplet ejection amount is shown. The intervals between the drive pulses were TN1 = 9.0 microseconds, TN2 = 8.9 microseconds, TN3 = 8.7 microseconds, and TN4 = 7.8 microseconds.

  In this way, the interval between the first drive pulse and the second drive pulse is extended to such an extent that the droplets are not separated. Assuming that the drive pulse interval at that time is TN1, TN1 is set to 1.2 to 1.3 × Tc, and the drive pulse interval after the second drive pulse is gradually narrowed to optimize the ink droplet ejection speed. Was confirmed not to change significantly. Here, the drive pulse interval TN is selected so that the plurality of ink droplets are approximately united when the printing gap is about ½ of the print gap of 1 mm.

  FIG. 11 shows a flight state when TN1 = 11.0 microseconds (≈1.5 × Tc) and five consecutive drive pulses are applied while the subsequent drive pulse intervals are sequentially reduced. Thus, it was found that even when TN1 = 1.5 × Tc, the ink droplets were combined as one ink droplet in the vicinity of the printing gap of 1 mm.

  Summing up the above results, if the drive pulse interval between the first drive pulse and the second drive pulse is TN1, and the subsequent drive pulse intervals are TN2, TN3,..., TNn (n is a natural number), TN1 (= 1.2 × Tc to 1.5 × Tc)> TN2> TN3>...> TNn ≧ Tc.

  FIG. 12 is a diagram showing how ink droplets are ejected using a flow 3D of analysis software, modeled on the ink flow path of the head used in the ink jet recording head according to the present invention, every 1 microsecond. The drive pulse used in this analysis is an application of an expansion time Tf = 2 microseconds, a holding time Th = 2.5 microseconds, and a contraction time Tr = 2 microseconds. When the expansion time Tf of the drive pulse is applied, the meniscus is drawn into the nozzle opening 11. After a predetermined time holding process Th, the ink jumps out to the nozzle opening by the Tr contraction process. In this process, the ink in the nozzle opening 11 jumps out so as to overflow to the surface of the nozzle plate 10 which is the air release surface. If the interval until the next drive pulse is long, the protruding ink is eventually drawn by the negative pressure in the nozzle. However, when a plurality of drive pulses are applied at short intervals, the overflowed ink will overflow the next ink before being drawn into the nozzle opening 11. If a large amount of ink adheres to the vicinity of the nozzle opening 11, the straightness of the ink droplet flight may be impaired.

Table 1 below is a table showing the contact angle between the surface of the nozzle plate 10 and the ink and the ejection abnormality. The hatched portion in this table is the contact angle at which ejection failure has occurred.

  As is apparent from this table, it can be seen that if the contact angle between the surface of the nozzle plate 10 and the ink is 65 ° or more, ejection failure does not occur, and in order to ensure the reliability of ink ejection, It has been found that it is desirable for the angle to be greater than 70 °. The upper limit of the contact angle is not particularly specified, but about 85 ° is appropriate.

  By restricting the contact angle to 65 ° or more in this way, ink overflow can be prevented, ink droplets can be kept straight, and print quality can be improved. Here, as the water-repellent treatment film coated on the surface of the nozzle plate 10, for example, a fluorine-based resin, a silicone-based resin, or the like is used. However, the material is not particularly limited as long as the material can ensure a contact angle with ink. Absent.

  Needless to say, it is desirable that ink droplets ejected by a plurality of drive pulses merge during flight. However, in an inkjet-type wide format printing apparatus used for signboard printing for outdoor use, the printing gap between the surface of the nozzle plate 10 and the recording medium 100 is a printing gap such as an inkjet recording apparatus for office use or consumer use. Even if it is larger than about 1 mm, it is about 1.5 mm to 2 mm. Furthermore, when a large droplet, for example, an ink droplet of 30 picoliter (pl) or more is required, the number of applied driving pulses increases. As a result, a plurality of droplets may not coalesce within 1 mm of the printing gap. Therefore, the interval between the drive pulses may be adjusted so that the number of drive pulses is united when flying to 1.5 mm, or in some cases, about 2 mm.

FIG. 13 shows an image when ink droplets that are continuously driven land on a recording medium. A recording medium formed by landing at the velocity V1 of the leading ink droplet, where Ts is the time difference from the arrival of the leading ink droplet of the plurality of ink droplets to the recording medium until the trailing ink droplet lands on the recording medium. The dot diameter D2 formed by the upper dot diameter D1 and the velocity V2 of the last ink droplet, and the speed of the recording medium on which the ink droplets land in the line head type device in which the inkjet recording head 1 is fixed in a line, or Assuming that the serial type carriage speed at which the carriage on which the inkjet recording head 1 is mounted performs printing while reciprocating is Vp and the distance from the center of the first droplet to the center of the last droplet is Ln, the time difference Ts between the droplet and the tail of the droplet, Ts = Ln / Vp details Ts = Ln / Vp = {( 1/2) × (D1 + D2 + D3 + ·· Dn + D (n + 1) )} / Vp so below, the respective drive pulse interval may be set in a range of 1.2 × Tc~1.5 × Tc. As a result, the ink droplets that have landed on the recording medium are not separated at least and dots are formed. If the dots are separated, the printed color density will be different, or the ridgeline portions of characters and images will be unclear, resulting in a decrease in print quality.

  By doing so, the traces of ink droplets landing on the recording medium are as shown in FIG. The ink that has landed on the recording medium generally does not dry immediately. Therefore, when a subsequent ink droplet collides, a force to gather is exerted by the surface tension of the ink. As a result, the actual landing shape is formed as one dot so that it becomes a slightly elongated dot.

  FIG. 14 is a cross-sectional view of the ink jet recording head 1 according to the second embodiment of the invention. This embodiment is different from the first embodiment shown in FIG. 1 in that a heater 200 for heating ink is installed on a side surface of the high-rigidity plate 70 facing the opening groove 72.

  The heater 200 is controlled by a power source and a control device (not shown) so that the recording head 1 is maintained at a certain temperature higher than the atmospheric temperature, for example, 40 ° C. to 80 ° C. The heater 200 can maintain the recording head 1 and ink in the head at a substantially constant temperature. As a result, even if the ambient temperature of the ink jet recording apparatus changes, the viscosity of the ink can be maintained substantially constant by maintaining the ink at a substantially constant temperature. The viscosity of the ink changes depending on the temperature, and the flying state of the ink drop may change due to the change. By attaching the heater 200 to the recording head 1 as in the present embodiment, it is possible to provide an ink jet recording apparatus in which stable flying of ink droplets is always maintained, and print quality is not impaired by changes in the surrounding environment. it can.

  Also in the recording head 1 of the present embodiment, the same effect as that of the first embodiment can be obtained by performing water repellent treatment on the surface of the nozzle plate 10.

  Four recording heads 1 described in the first and second embodiments are provided, and each recording head 1 is separately loaded with cyan, magenta, yellow, and black inks, and the inks are ejected, and the respective colors are superimposed on the recording medium. Thus, a color image can be formed.

  In the above embodiment, the case of the ink jet recording apparatus has been described. However, the present invention is not limited to this. For example, a color material solution used for manufacturing a color filter of a liquid crystal display, or an electrode film formation such as an organic EL display The present invention can also be applied to a droplet discharge apparatus that discharges a special liquid such as an electrode material liquid used in the above.

1 is a cross-sectional view of a multilayer ink jet recording head according to Embodiment 1 of the present invention. FIG. 4 is a diagram for explaining the principle of ink droplet ejection of the recording head. It is a wave form diagram which shows the example of the drive pulse applied for the single ink drop to the recording head. FIG. 6 is a diagram illustrating a state in which an ink meniscus is observed at a nozzle opening of the recording head and a driving voltage thereof. 1 is a perspective view of an ink jet recording apparatus according to an embodiment of the present invention. It is a wave form diagram which shows the example of the continuous drive pulse applied to the recording head. FIG. 6 is a diagram showing the relationship between the number of drive pulses and the speed of ink droplets when drive pulses are applied to the recording head at each fixed period. It is a figure which shows the flight state of the ink drop on the drive conditions shown by FIG. FIG. 6 is a diagram illustrating a relationship between an ink droplet flying state, the number of drive pulses, and an ink droplet ejection speed when the recording head is driven with five continuous drive pulses. FIG. 6 is a diagram illustrating the flying state of ink droplets when the recording head is driven with five continuous driving pulses under different driving conditions, the relationship between the number of driving pulses and the speed of ink droplets, and the relationship between the number of driving pulses and the amount of ink droplets. . FIG. 6 is a diagram illustrating a flying state of ink droplets when five continuous drive pulses are applied while sequentially decreasing the drive pulse interval applied to the recording head. FIG. 4 is a diagram showing, every 1 microsecond, a state in which an ink flow path of a head used in an ink jet recording head according to the present invention is modeled and ink droplets are ejected by using Flow 3D of analysis software. FIG. 6 is a diagram showing an image when ink droplets driven continuously by the recording head land on a recording medium. FIG. 6 is a cross-sectional view of a multilayer ink jet recording head according to Embodiment 2 of the present invention.

Explanation of symbols

1: Recording head 5: Flow path substrate 6: Ink 7, 7a, 7b: Drive pulse 8: Ink droplet 9: Drive pulse 9a: Drive pulse corresponding to time Tf 10: Nozzle plate 11: Nozzle opening 20: Chamber plate 21 : Communication channel 30: restrictor plate 31: pressure generating chamber 32: restrictor 33: opening 40: diaphragm plate 41: diaphragm 50: support plate 52: common ink reservoir 60: filter plate 61: filter 70: high Rigid plate 71: Common ink chamber 72: Opening groove 80: Piezoelectric actuator 81: Piezoelectric vibrator 82: Support member 83: Drive control unit 100: Recording medium 101: Sub ink tank 102: Head maintenance unit 103: Main ink tank 104: Supply tube 105: cap 110, 111: guide shaft 20 : Heater.

Claims (20)

A nozzle opening provided for discharging liquid, a pressure generating chamber provided in communication with the nozzle opening, pressure generating means for expanding and contracting the volume of the pressure generating chamber, and A droplet discharge head having a liquid resistance portion provided in the middle of a liquid flow path for supplying a liquid;
A drive control unit that applies a drive pulse for expanding and contracting the volume of the pressure generating chamber to the pressure generating unit;
Two or more drive pulses are continuously applied from the drive control unit at a predetermined interval to the pressure generating means, and the liquid droplets ejected according to the number of drive pulses substantially before reaching the adherend. In a droplet discharge device that merges into one droplet and reaches the adherend medium,
The drive control unit
Output drive pulses with the same pulse shape,
When the period of the natural frequency determined by the liquid flow path from the nozzle opening to the fluid resistance part is Tc, the pulse width Tp of the drive pulse is set smaller than the period Tc (Tp <Tc),
When the pulse interval from the start of the nth pulse to the start of the (n + 1) th pulse of n consecutive (n ≧ 2) integer driving pulses is TNn, the first pulse with n = 1 and n = 2 The pulse interval TN1 with the second pulse is set in a range of 1.2 × Tc to 1.5 × Tc, and the pulse interval TN2 after the pulse interval TN2 between the second pulse and the next third pulse is set. , TN3,... TNn is smaller than TN1 and set to a period Tc or more of the natural frequency of the liquid flow path (TN1 = 1.2 × Tc to 1.5 × Tc> (TN2, TN3 ,... TNn ≧ Tc). 2. The liquid droplet ejection apparatus according to claim 1, wherein the pulse interval after the pulse interval TN <b> 2 is sequentially reduced, and the final pulse interval TNn is set to be equal to or greater than the period Tc of the natural frequency of the liquid channel. (TN2> TN3>...> TNn ≧ Tc). 3. The droplet discharge device according to claim 1, wherein the drive pulse includes an expansion time Tf in which a voltage is raised in order to expand the volume of the pressure generating chamber, and a holding time in which the raised voltage is held constant. A droplet discharge device having a trapezoidal waveform having Th and a contraction time Tr for decreasing a voltage in order to contract a volume of a pressure generating chamber. 4. The droplet discharge device according to claim 3, wherein the total time Tw of the expansion time Tf and the holding time Th is drawn into the meniscus by the expansion of the pressure generating chamber, and the drawing position of the meniscus becomes approximately ½. A droplet discharge device characterized by being within a time range from the point until the meniscus position first becomes the lowest point. 5. The droplet discharge device according to claim 1, wherein a contact angle of the surface of the nozzle opening with respect to the liquid is 65 ° or more. 6. 6. The liquid droplet ejection apparatus according to claim 1, wherein a plurality of liquid droplets ejected according to the number of drive pulses are ½ of a distance from the nozzle opening to the adherend medium. A droplet discharge device characterized by forming a single droplet in a range from a place exceeding the above to the adherend medium. 6. The liquid droplet ejection apparatus according to claim 1, wherein a plurality of liquid droplets ejected in accordance with the number of driving pulses has a distance from the nozzle opening to the deposition medium of 0.5 mm. A droplet discharge device characterized by forming one droplet within a range of ˜2 mm. 8. The liquid droplet ejection apparatus according to claim 1, wherein the first liquid droplet discharged from the plurality of liquid droplets ejected in accordance with the number of drive pulses reaches the last of the adherend medium. The time difference until the liquid droplets land on the adherent medium is Ts, and the speed of the adherent medium of the line head type device or the serial type carriage speed is Vp. A liquid droplet ejection apparatus, wherein the time difference Ts between the first liquid droplet and the last liquid droplet is Ts = Ln / Vp or less , where Ln is the distance to the center of the liquid droplet. 9. The droplet discharge apparatus according to claim 1, wherein a heater is installed in the droplet discharge head, and the temperature is controlled so that the viscosity of the discharged liquid is substantially constant. A droplet discharge apparatus characterized by the above. A nozzle opening provided for discharging liquid, a pressure generating chamber provided in communication with the nozzle opening, pressure generating means for expanding and contracting the volume of the pressure generating chamber, and A liquid droplet ejection head having a liquid resistance portion provided in the middle of a liquid flow path for supplying liquid;
Two or more drive pulses are continuously applied to the pressure generating means at a predetermined interval, and the liquid droplets ejected in accordance with the number of drive pulses become substantially one liquid droplet before reaching the adherend medium. In a droplet discharge method that combines and reaches the adherend medium,
The successive drive pulses have the same pulse shape;
When the period of the natural frequency determined by the liquid flow path from the nozzle opening to the fluid resistance part is Tc, the pulse width Tp of the drive pulse is set smaller than the period Tc (Tp <Tc),
When the pulse interval from the start of the nth pulse to the start of the (n + 1) th pulse of n consecutive (n ≧ 2) integer driving pulses is TNn, the first pulse with n = 1 and n = 2 The pulse interval TN1 with the second pulse is set in a range of 1.2 × Tc to 1.5 × Tc, and the pulse interval TN2 after the pulse interval TN2 between the second pulse and the next third pulse is set. , TN3,... TNn is smaller than TN1 and set to a period Tc or more of the natural frequency of the liquid flow path (TN1 = 1.2 × Tc to 1.5 × Tc> (TN2, TN3 ,... TNn ≧ Tc). 11. The droplet discharge method according to claim 10, wherein pulse intervals after the pulse interval TN <b> 2 are sequentially reduced, and the final pulse interval TNn is set to be equal to or greater than the period Tc of the natural frequency of the liquid channel. (TN2> TN3>...> TNn ≧ Tc). 12. The droplet discharge method according to claim 10, wherein the drive pulse keeps the rising voltage constant and the time Tf of the expansion step for raising the voltage to expand the volume of the pressure generating chamber. A droplet discharge method characterized by having a trapezoidal waveform shape having a holding process time Th and a contraction process time Tr for decreasing the voltage in order to contract the volume of the pressure generating chamber. 13. The droplet discharge method according to claim 12, wherein a total time Tw of the expansion process time Tf and the holding process time Th is drawn by the expansion of the pressure generating chamber, and the meniscus drawing position is approximately 1. A droplet discharge method characterized by being within a time range from the point at which / 2 is reached until the meniscus position first becomes the lowest point. 14. The droplet discharging method according to claim 10, wherein a contact angle of the surface of the nozzle opening with respect to the liquid is 65 ° or more. 15. The liquid droplet ejection method according to claim 10, wherein a plurality of liquid droplets ejected in accordance with the number of driving pulses are ½ of a distance from the nozzle opening to the deposition medium. A droplet discharge method characterized in that one droplet is formed in a range from a place exceeding the above to the adherend medium. 16. The droplet discharge method according to claim 10, wherein a plurality of droplets discharged according to the number of drive pulses has a distance from the nozzle opening to the deposition medium of 0.5 mm. A droplet discharge method characterized by forming a single droplet within a range of ˜2 mm. 16. The droplet discharge method according to claim 10, wherein the first droplet of the plurality of droplets discharged according to the number of drive pulses reaches the last of the deposition medium. The time difference until the liquid droplets land on the adherent medium is Ts, and the speed of the adherent medium of the line head type device or the serial type carriage speed is Vp. A droplet discharge method, wherein a time difference Ts between a first droplet and a last droplet is Ts = Ln / Vp or less , where Ln is a distance to the center of the droplet. 18. The droplet discharge method according to claim 10, wherein a heater is installed in the droplet discharge head, and the temperature is controlled so that the viscosity of the discharged liquid is substantially constant. A droplet discharge method characterized by An image forming apparatus comprising the liquid droplet ejection apparatus according to claim 1, wherein the liquid is ink and the landing medium is a recording medium. 20. The image forming apparatus according to claim 19, wherein a plurality of the droplet discharge heads loaded with inks of different colors are provided.

Images